This application addresses broad Challenge Area (03) Biomarker Discovery and Validation, and specific Challenge Topic, 03-MH-101 Biomarkers in mental disorders. The variability of treatment outcome in PTSD, the high risk of relapse and the fact that only a subset of trauma victims develop PTSD are unsolved aspects of the illness. Yet at the current time there are no tests or markers that can help guide treatment decisions about which treatment should be administered to a particular patient, how long the person should be treated or whether trauma victims at high risk can be identified early, prior to the onset of illness. We have therefore developed a model of emotional circuitry abnormalities in PTSD. With funding of the current application we propose to validate these abnormalities as biomarkers in PTSD that can be further developed to guide treatment decisions. Post Traumatic Stress Disorder (PTSD) is a common, severe psychiatric problem that occurs in some people following a traumatic event. Treatment outcomes are variable and incomplete. Relapse is common. Brain biomarkers of abnormal emotional circuitry could provide evidence of insufficient treatment and high risk for relapse. Biomarkers could identify subgroups of patients who are better suited to a particular treatment.